A plan to send live microbes to the Red Planet's largest moon risks wrecking our search for extraterrestrial life, argues Barry E. DiGregorio.

We humans have a unique talent for contaminating pristine environments. We put millions of tonnes of pollutants into the atmosphere every year. We poison our soils, lakes, rivers and streams with chemical and radioactive waste. We spill oil into our seas. We fill the Pacific and Atlantic oceans with islands of plastic garbage visible from space. Is it any surprise that we are also contaminating pristine celestial bodies with bacterial spores?

Spacefaring nations have been sending unsterilised spacecraft to the moon, Mars, Jupiter, comets and asteroids for over 40 years. It has been estimated that about one trillion microbial spores from spacecraft are now scattered around Mars (Advances in Space Research, vol 35, p 1648). Yet the search for life in our solar system has barely begun.

It wasn't always so. At the dawn of the space age, policy-makers had every intention to protect space from contamination. They also set out to protect Earth from material brought in from other celestial bodies that might contain toxins or pathogens.

These lofty goals were enshrined in the United Nations Outer Space Treaty of 1967, now signed by all spacefaring nations. It plainly states: "Parties to the Treaty shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter."

Early spacecraft had to be thoroughly and expensively sterilised before they could be sent to the moon or planets. However, over the years this requirement has been watered down. The Committee on Space Research (COSPAR) in Paris, France, has been charged with making adjustments based on new data. COSPAR now allows spacecraft to bypass any sterilisation as long as they are not carrying life-detection instruments or landing on areas of Mars designated as "special regions" - areas where liquid water could exist for short periods that might support terrestrial microbial growth. The problem with these policy changes is that they are premature: our knowledge about the survivability of life on Mars is constantly changing with each spacecraft mission.

Numerous reports have debated whether terrestrial spores might be able to replicate and spread on Mars. We still don't know the answer, so why risk contaminating the most Earth-like planet in our solar system?

Now a mission slated to launch in the second half of 2011 will effectively tear up the treaty. The Russian Federal Space Agency's Phobos Sample Return Mission (formerly known as Phobos-Grunt) will send not just microbial spores but live bacteria into the solar system for the first time. If this isn't a direct violation of the Outer Space Treaty then what is?

The mission will fly to Mars, study it from orbit and then land on Phobos, the larger of Mars's two moons. On board will be two sealed capsules containing live micro-organisms. Some months later the craft will embark on the return journey carrying the still-sealed capsules, plus samples of soil scooped up from the surface of Phobos. All being well it will return to Earth in 2014.

The reason for sending live micro-organisms to Phobos is to investigate if any survive the three-year journey. If they do, the researchers say it would support the theory of transpermia, which holds that microbial life can be exchanged between planets via rocks ejected from their surfaces by collisions.

That theory is tenuous at best. All of the Martian meteorites found on Earth spent millions of years in space before they arrived. In order to justify their experimental goals, one of the groups involved in the experiment, The Planetary Society of Pasadena, California, argues that rocks larger than 100 grams are transferred from Mars to Earth in only two to three years. No direct evidence exists for this claim. Is the transpermia question really so important that it is worth risking the contamination that would surely happen if the spacecraft malfunctioned and crashed on Mars?

This is no small risk. Of 38 craft launched towards Mars, only 19 succeeded. At least three crash-landed on the planet's surface.

Of 38 craft launched towards Mars, only 19 made it. At least three crash-landed on the surface

The Phobos Sample Return Mission has one of the most complex mission profiles ever flown. Not only will the spacecraft have to perform a series of manoeuvres in Mars orbit to launch a satellite, it will also have to change its orbit to rendezvous with Phobos. The last time the Russians attempted to land on Phobos was in 1988 with the Phobos 1 and 2 spacecraft. Both lost contact en route.

To make matters worse, we already know a good deal about microbial survival in space thanks to experiments done with Apollo, the Mir space station, the International Space Station and the space shuttles. Similar experiments have also been done at space environment simulation facilities on Earth. Why not continue to use these and spare Mars potential contamination?

For those having any doubts about microbes surviving a fiery re-entry, you need only consider the break-up of the Columbia space shuttle in February 2003. One of the microbial experiments on Columbia survived intact, although slightly charred. After analysis it was determined that a heat-resistant microbe, Microbispora, had survived.

The question "Is there life on Mars?" has surely been answered by our own ignorant actions. Yes, there is life on Mars, because we put it there. The only remaining question is, will it survive and grow, confusing future scientific results? Sending live bacteria to Phobos can only increase the risk that it will.